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Forecasters say temperatures could reach 27C in south east after just failing to break record on Tuesday

The UK is expected to bask in the hottest day of the year so far on Wednesday, forecasters say.

Temperatures could reach highs of 26C (78F) or 27C, according to MeteoGroup, the weather division of the Press Association.

The sunshine struggled to break through the cloud on Tuesday, and the highest temperature recorded was 24C in Manchester – slightly below the high of the year which was 25C on 6 June in Lee-on-Solent, Hampshire.

Matt Dobson, a forecaster at Meteogroup, said hopes of record-breaking heat were dashed by cloud on Tuesday, but he was more optimistic about Wednesday.

He said on Tuesday: "There were suggestions that the south-east could have seen temperatures get to 25C but we've seen a lot of cloud lingering. It's knocked the temperatures on the head. Tomorrow we've a better chance of beating 25C. It's more likely to happen in the London area or a few locations to the south and west of London."

Dobson said this would be "sensitive to how much cloud there will be", but there was a good chance it would be the hottest day of the year.

Further north, temperatures will remain lower, with the driest weather expected in Wales, Northern Ireland and northern England. North-west Scotland would be the coolest region, Dobson said.

The welcome warm blast follows what the Met Office said was the coldest spring since 1962, with a mean temperature across March, April and May of 6C, 1.7C below the long-term average.

On Monday, scientists gathered at an unprecedented meeting of meteorologists and climate scientists convened by the Met Office to discuss the UK's recent unseasonal weather. They said Britain could face five to 10 years of washout summers.

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Forecast that Britain could be in middle of 10-20 year 'cycle' of wet summers delivered following gathering at Met Office

Don't worry, summer is on its way – but you might have to wait until 2023.

As the prospect of another gloomy Glastonbury and wet Wimbledon looms, leading climate scientists have warned that the UK could be set for a further five to 10 years of washout summers.

The grim conclusion was delivered after an unprecedented gathering of scientists and meteorologists at the Met Office in Exeter to debate the range of possible causes for Europe's "unusual seasonal weather" over recent years, a sequence that has lasted since 2007.

Many will have hoped for news of sunnier times ahead. But after experts brainstormed through the day they delivered the shock finding that the UK could be in the middle of a 10-20 year "cycle" of wet summers. The last six out of seven summers in the UK have seen below-average temperatures and sunshine, and above-average rainfall.

Stephen Belcher, head of the Met Office Hadley Centre and professor of meteorology at the University of Reading, stressed that the finding was not an official long-term forecast and does not automatically mean the UK will now have a further decade of wet summers. But, he said, the scientists' conclusion was that the chances of this occurring are now higher than they first thought.

"Predicting when this cycle will end is hard," said Belcher, who led the meeting of 25 scientists. "We have seen similar patterns before – in the 1950s and the 1880s – and we have hints that we are coming towards the end of this current cycle. However, it might continue for the next five to 10 years. There is a higher probability of wet summers continuing. But it's very early days in trying to understand why this is happening."

The scientists must now address what "dynamical drivers" are causing this cycle, Belcher said. The meeting debated a range of possible interconnected reasons for the unusual weather of recent years, including this year's cold spring and the freezing winter of 2010/11. The most likely cause for the wet summers, he said, was the Atlantic multi-decadal oscillation, or AMO, a natural pattern of long-term changes to ocean currents.

Other candidate causes that could be "loading the dice", as Belcher described it, include a shift in the jet stream, solar variability and fast-retreating Arctic sea ice. Aggravating all of these factors could be the influence of anthropogenic greenhouse gases entering the atmosphere.

Dr James Screen, who studies how melting sea ice impacts on the jet stream at the University of Exeter, said: "There has been a lot of talk about declining Arctic sea ice playing a role in our weather patterns, but really that's just one aspect of changes in the Arctic climate – which has seen rapid warming compared to other parts of the world. Those changes mean there is less of a difference in temperature between the Arctic and tropics, which could impact the position of the jet stream."

The scientists also debated how melting sea ice should be better incorporated into climate models, as well as how observational data – for example, deep-ocean temperatures – could be improved to help their understanding of the potential relationship between climate change and the recent run of inclement weather and record-breaking extremes.

Len Shaffrey, a climate modeller based at the University of Reading who is also currently investigating possible links between Arctic sea ice retreat and European weather, said: "There are some fascinating science questions emerging about the influences on our weather, for example, from natural variations in ocean temperature. There is also some evidence that the record low amounts of Arctic sea ice have influenced patterns of European and British weather, but this evidence is not yet conclusive either way."

The scientific debate about the role of the jet stream – the fast "river" of meandering, 10km-high air which greatly determines UK weather - is intensifying. This week researchers from the University of Sheffield published a study in the International Journal of Climatology showing how "unusual changes" to the jet stream caused the "exceptional" melting of the Greenland ice sheet during the summer of 2012. Scientists say they must now determine what is causing these "displacements", as they are known, in the jet stream.

Tourist bosses were trying to find silver linings. David Leslie, a spokesman for the tourism agency Visit Britain, said people did not come to the UK for the weather alone. "The weather here is as unpredictable as anywhere else," he added.

"The days of the UK being seen as a foggy, wet destination have passed. Hot, cold or mildly pleasant, the weather is not a deterrent for overseas visitors coming here to enjoy Britain's tourism offering, which remains the best in the world."

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Costa Coffee benefits from cold spring – but Beefeater and Brewers Fayre suffer

Sales at Whitbread, the parent company of Costa Coffee and Premier Inn, rose in the first quarter as the coldest spring since 1962 hit its restaurant business but drove customers into its coffee shops.

The FTSE 100 company reported a 13.8% rise in total sales in the 13 weeks to 30 May, with like-for-like sales up 3.1%.

Costa benefited from the unseasonably chilly weather, with total sales jumping 23% to £281.8m, and like-for-like sales up 8%.

Whitbread said the restaurants division struggled in the early part of the quarter because of the chill. Total sales in the division rose 2.6%, with like-for-like sales flat.

Andy Harrison, chief executive, said: "We have seen a substantial improvement in our restaurants in recent weeks as the weather returns to something like normality."

Premier Inn, its budget hotel chain, managed a 12.7% increase in total sales and a 2.7% increase in like-for-like sales, despite being set against strong comparatives in London last year.

Harrison said: "Whitbread had a good start to the new financial year. We see no change to market conditions. Our plans for profitable organic growth are well established which, combined with our strong focus on returns, should create further substantial shareholder value," he said.

In April the group unveiled ambitious plans for growth over the next five years, targeting a 45% increase in the number of Premier Inn rooms to around 75,000, and a doubling of the size of Costa sales to £2bn.

It compared with a previous target of 65,000 rooms and Costa sales of £1.3bn.

Whitbread opened 39 new Costa shops in the UK in the first quarter, and a further 21 overseas, including 18 in China. There are a total of 271 Costa stores in China.

The group said it planned to open 300 net new Costa stores in the full year.

Whitbread, whose brands include Beefeater and Brewers Fayre, employs more than 40,000 people and serves over 22 million customers every month.

"Whitbread has delivered its almost customary breath of fresh air in the midst of a tepid economic backdrop," said Richard Hunter, head of equities at Hargreaves Lansdown stockbrokers.

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Meteorologists and scientists to try to figure out if icy winters and wet summers are due to natural variation or climate change

Leading scientists and meteorologists are meeting at the Met Office to discuss the UK's unusual weather patterns in recent years.

Experts will discuss the reasons for 2010's icy winter, last year's washout summer and this year's spring, which is set to be the coldest in more than 50 years.

Discussions at the Met Office in Exeter on Tuesday will seek to answer whether the unusual seasons were the result of natural variation or linked to the effects of climate change, such as melting Arctic sea ice.

Stephen Belcher, head of the Met Office Hadley Centre and chairman of the workshop, said: "We have seen a run of unusual seasons in the UK and northern Europe, such as the cold winter of 2010, last year's wet weather and the cold spring this year.

"This may be nothing more than a run of natural variability, but there may be other factors impacting our weather. For example, there is emerging research which suggests there is a link between declining Arctic sea ice and European climate – but exactly how this process might work, and how important it may be among a host of other factors, remains unclear.

"The Met Office is running a workshop to bring together climate experts from across the UK to look at these unusual seasons, the possible causes behind them, and how we can learn more about those drivers of our weather."

The meeting will assess the research done so far and discuss what needs to be studied in the future to get a better idea of what could be causing the weather extremes.

Earlier this month the Met Office said below-average temperatures through March, April and May made it the fifth coldest spring in national records dating back to 1910 and the coldest spring since 1962.

Provisional findings show the UK's mean temperature for the season was 6C (42.8F), while March was "exceptionally" cold, averaging 2.2C.

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